A Non-Invasive Method for the Estimation of Inter-Turn Short-Circuit Currents in Induction Motors

Inter-turn faults (ITF) progress to catastrophic failures faster than other common induction motor (IM) faults, which can lead to high downtime costs if replacement units are not available upon detection. However, ITFs do not progress identically fast in all motors, as the early-stage ITF currents are not equally severe. Therefore, considering this and that storing replacements for every unit is impractical and very costly, a tool that helps to determine which motors will require a replacement unit ready upon fault detection becomes essential for industry to mitigate downtime costs. This paper proposes a fast and noninvasive method to estimate the short-circuit current for any given load level, short-circuit position, contact resistance and low percentage of shorted-turns. The method is validated against finite element calculations and real measurements showing great accuracy. Moreover, it allows to easily calculate the short-circuit current maps, a tool that helps to analyze how severe the earlystage ITF short-circuit currents are in a given motor. Finally, it proposes a new indicator derived from these maps, that helps the end-user to assess the severity of these currents, and thus decide whether to have or not a replacement unit ready.